Monochromatic Beam Profiling Monitor
This detector is currently developed in a collaboration with the detectors group at PSI (CH).
First prototypes will be soon available for test purposes, please contact us for more details.
Current commercially available in-line X-ray monitors use 2x2 pixel-arrays to detect the beam position but fail in providing any information about beam profiles. This information would be extremely useful in several applications such as spectroscopic measurements where, thanks to the increased brightness and coherence of the next generation X-ray beams, it will be for example possible to collect fast XAS (x-ray absorption spectroscopy) data by synchronously quickly rotating the monochromator and, at the same time, changing the undulator gap. In order to ensure a stable focused x-ray beam on the sample while the optical elements are moving these measurements will require a feedback not only of the beam position but also of its 2D profile. In more general terms, beam profile monitoring would significantly improve the overall stability of various types of long-term imaging and/or spectroscopic experiments compensating mechanical systematic drifts or instabilities. Although some diamond-based segmented detectors have been tested in the past (see e.g. [[1], [2]]), no systems are commercially available due either to low material qualities (polycrystalline diamond) or limited chip sizes (single crystal CVD diamond) of available diamond sensors. Recently Silicon Carbide (SiC) free-standing membranes have been validated for hard-Xray Beam Position Monitoring (XBPM), as an alternative to Diamond ones [[3]].
SiC XBPMs of thicknesses of 0.2 µm, 1µm, 2µm, 10µm and 20µm are now commercialized available by SenSiC.ch.
In the next months we aim at the demonstration of a detection system, based on SiC free-standing membranes, capable of in-situ and real-time characterization of the beam profile. Fig.1 show front and back view of a SiC pixelated sensor based on a free-standing membrane where the active region of the detection system is an array of 16x16, 100 µm x 20 µm, pads located on the SiC membrane. Signals from the 256 pixels are read out by two Gotthard-II charge-integrating readout ASICs (Application Specific Integrated Circuit), which was originally developed for silicon strip sensors for the European XFEL. The architecture of the Gotthard-II ASIC is shown in Fig.2. It has three gains which can be selected automatically through its dynamic gain switching logic. The dynamic range is up to 35 Me- with good linearity. Thanks to its on-chip ADCs (Analogue-to-Digital Converter), it provides a frame rate above 400 kHz allowing for real time analysis of the X-ray beam profile: From the profile data, the beam shape as well as the beam position can be derived in a non-destructive manner, which allows using the sensor in a feed-back loop and optimizing the focal spot. The design and fabrication of the pixelated SiC sensors, as well as preliminary results from complete devices obtained at the OPTICS beamline of the Swiss Light Source, will be presented at next Synchrotron and Radiation Instrumentation (SRI2021) conference in Hamburg.
Fig.1 Front and rear view of a SiC pixelated sensor
Fig.2 Simplified block diagram of the GOTTHARD chip [1].
[1] A. Mozzanica et al., Journal of Instrumentation 7 (2012)
[2] T. Zhou et al., J. Synchrotron Rad. 22, 1396 (2015)
[3] S. Nida et al J. Synchrotron Rad. 26, 28 (2019)
